Many types of electronic systems have one or more fans to help cool the electronic devices. Temperature sensors included in the systems are used to obtain the temperature readings. The system adjusts the fan speed based on the temperature readings. As the system temperature increases, fan speed is set to a higher speed to keep all electronic devices operate within their specifications. Fan speed thus is a function of temperature.
Some systems have a static environmental policy which remains fixed during runtime. In a static environmental policy method, the electronic system's central processing unit (CPU) constantly polls temperature sensors and sets the proper fan speeds based on the sensed temperature. While a static method is simple to implement, a static method may be inadequate for electronic systems whose configurations are not static. Some electronic systems may be capable of accepting additional field replaceable units (FRUs) during runtime, or existing FRUs may be removed during runtime. The ability to add and/or remove FRUs during run-time may change the thermal characteristics of the system. The system software must be constantly upgraded to support new FRUs. As the types of new FRUs increase or system operating ranges change, the FRU combination complexity and thermal policy can grow exponentially. As the overhead of CPU housekeeping tasks increases, the CPU's main job to control the main operations of the system (e.g., a network switch) will be impaired and cause overall system performance degradation.